In the conventional image interpolation mechanism, a motion vector of a block in an interpolated frame is determined by a block matching algorithm, and the block is generated according to the motion vector. FIG. 1 shows a schematic diagram of the block matching algorithm. Frames Fn−1 and Fn are two successive input image frames, and an interpolated frame FI is generated by the conventional image interpolation mechanism between frames Fn−1 and Fn. Areas R4 and R5 respectively are part of the foreground object of the frames Fn−1 and Fn, and other areas belong to the background image. A first reference motion vector MV1 in FIG. 1 represents the moving direction of the foreground object, and a second reference motion vector MV2 represents the moving direction of the background image. In addition, an area R3′ in the frame Fn is covered by the foreground object in the frame Fn−1 and thereby not presenting in the frame Fn−1. Likewise, an area R6′ of the frame Fn−1 is covered by the foreground object in the image frame Fn and thereby not presenting in the frame Fn. Therefore, when the motion vector is determined via the conventional block matching algorithm, areas R1, R2, R7 and R8 are observed in the background images of the two frames Fn−1 and Fn, and the areas R4 and R5 covered by the foreground objects are observed in the two frames Fn−1 and Fn, so as to accurately determine a target motion vector, and to accurately generate the image areas R1, R2, R4, R5, R7 and R8 in the interpolated frame FI as shown in FIG. 1.
However, when target motion vectors of areas R3 and R6 in the interpolated frame FI are determined, since the area R3 in the interpolated frame FI only presents in an area R3′ of the frame Fn but not in the image frame Fn−1, the conventional block matching algorithm does not work to find a true motion vector for the area R3 from the two frames Fn−1 and Fn. Likewise, since the area R6 in the interpolated frame FI only presents in an area R6′ of the frame Fn−1 but not in the frame Fn, the conventional block matching algorithm does not work to find a true motion vector for the area R6 from the two frames Fn−1 and Fn. Therefore, when the motion vector is determined via the conventional block matching algorithm, an overall quality of the interpolated frame FI is reduced due to the uncovered area R3 and the covered area R6.
Theoretically, both motion vectors of the areas R3 and R6 in the interpolated frame FI are the motion vectors of the background image, so that the corresponding background images are accurately displayed on the areas R3 and R6. For example, the second motion vector MV2 is adopted to determine the image of the area R3 from the area R3′ of the frame Fn, and the second motion vector MV2 is also adopted to determine the image of the area R6 from the area R6′ in the frame Fn−1. Therefore, the block matching algorithm cannot determine the accurate motion vectors for the uncovered area R3 and the covered area R6, thus causing image distortions of the interpolation areas R3 and R6. When the block matching algorithm is applied to frame rate conversion, image quality of the frame is significantly reduced by using the conventional image interpolation mechanism.